Commuters pass through the turnstiles at the Powell St. BART station in San Francisco, CA Tuesday, October 22, 2013. BART service was restored system wide after management and union workers reached an agreement on a new contract.

Photo: Michael Short, The Chronicle

Commuters pass through the turnstiles at the Powell St. BART...

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Commuters pass through the turnstiles at the Powell St. BART station in San Francisco, CA Tuesday, October 22, 2013. BART service was restored system wide after management and union workers reached an agreement on a new contract.

Photo: Michael Short, The Chronicle

Commuters pass through the turnstiles at the Powell St. BART...

Image 3 of 6

Commuters pass through the turnstiles at the Powell St. BART station in San Francisco, CA Tuesday, October 22, 2013. BART service was restored system wide after management and union workers reached an agreement on a new contract.

Photo: Michael Short, The Chronicle

Commuters pass through the turnstiles at the Powell St. BART...

Image 4 of 6

Bay Area Rapid Transit passengers wait for a BART train to depart the Fruitvale station Tuesday, Oct. 22, 2013, in Oakland, Calif. A contentious, on-again, off-again Bay Area transit strike infuriated hundreds of thousands of commuters forced to wait hours for overcrowded buses and ferries and brought grave questions when two workers were killed. The labor clash now appears to be heading toward resolution, but unions now face calls to ban transit strikes, and political leaders are struggling to assure communities they won't be economically and socially jeopardized again by union disputes. (AP Photo/Ben Margot)

Photo: Ben Margot, AP

Bay Area Rapid Transit passengers wait for a BART train to depart...

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OAKLAND, CA - OCTOBER 21: A memorial honoring two Bay Area Rapid Transit (BART) workers who were struck and killed by a BART train over the weekend while servicing tracks near the Walnut Creek is seen at the West Oakland BART station on October 21, 2013 in Oakland, California. BART workers continue to strike after contract negotiations between BART management and the transit agency's two largest unions fell apart last week. Management and unions agreed on the financial specifics of the contract but differed on workplace safety rules. An estimated 400,000 commuters ride BART each day. (Photo by Justin Sullivan/Getty Images)

Photo: Justin Sullivan, Getty Images

OAKLAND, CA - OCTOBER 21: A memorial honoring two Bay Area Rapid...

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OAKLAND, CA - OCTOBER 21: Pedestrians walk by a closed Bay Area Rapid Transit (BART) station on October 21, 2013 in Oakland, California. BART workers continue to strike after contract negotiations between BART management and the transit agency's two largest unions fell apart last week. Management and unions agreed on the financial specifics of the contract but differed on workplace safety rules. An estimated 400,000 commuters ride BART each day. (Photo by Justin Sullivan/Getty Images)

BART is calling on its unions to reopen contract negotiations because of what its directors say is an expensive mistaken agreement on paid medical leave that now threatens to derail the pact that ended a four-day strike last month.

BART directors met in closed session Friday in a hastily called meeting to discuss what they call an unintended "error" in the contract that gives the system's workers up to six weeks of paid time off for personal or family health problems.

"We've reviewed the chronology of events concerning Section 4.8 and are convinced that it was never the district's intention to include the disputed Family Medical Leave Act proposal in the contract," Tom Radulovich, president of the BART board, said in a statement after the three-hour session. "We have directed the general manager to go back to the bargaining table and continue a discussion with union officials in an attempt to resolve the matter."

That's not the way the transit agency's unions see the matter, especially because their members have overwhelmingly ratified the contract, disputed clause and all.

Union officials brought with them a copy of the tentative agreement on the disputed contract section, signed in July by Tom Hock, BART's chief negotiator, Paul Oversier, the district's assistant general manager, and Rudy Medina, BART's department manager of labor relations. Hock, a consultant brought in to handle the contract negotiations, is no longer with the district, Radulovich said.

'Signed in error'

In a fact sheet distributed Friday, transit district officials said the medical leave proposal had been rejected twice in June but was included in a stack of tentative agreements "and signed in error by the district in July 2013. ... Since the district assumed that the proposal was not in play, the BART board never discussed it."

The error could be an expensive one, costing the district as much as $44.2 million over the four-year length of the contract, although other estimates provided to the directors were much lower.

"We are not comfortable with the potential liability that could result from the adoption of this contract provision," Radulovich said in the statement.

Up to now, BART workers have been allowed to take up to 12 weeks of job-protected leave to deal with serious personal or family medical problems or to bond with a newborn or newly adopted child, but they had to use sick leave, vacation days or other accrued time off. But under the disputed contract provision, BART would now pay for the first six weeks of that leave.

"If this had been something agreed to in the final hours, it would be more understandable," Steele said. "But this was signed in July, so it's not a last-minute deal."

The list of tentative agreements went back to BART negotiators in August and September and then on Oct. 25 when the entire list of signed agreements was again given to district officials, she said.

"They indicated there was a problem and asked us to pull the section," Bryant said. "We said that we had already signed off on it and that's clearly what they would have done to us."

Obligation to sign

While BART managers were unwilling to comment on the specifics of Friday's discussion, union leaders said they had been told transit district officials had recommended that the directors reject the contract when it comes before them for approval at a meeting on Thursday, unless the section in question is removed.

Speaking to the board before the closed session, Bryant said the directors had an obligation to sign the contract.

"There were no nefarious dealings, no glitches, no secretarial mistake," she said. "We have signed an agreement they gave to our members that BART was totally aware of."

"Maybe the people running the district don't know what they're doing," he told the BART board. "Now what you have is buyer's remorse, you bought it and now you want to return it. Well, there are no returns."

While it's not unusual to work out some contract details after an agreement is ratified, that can't happen unless the directors sign the contract, Steele said.

Until that happens, "we're not interested in modifying the language at all," she said. "An agreement is an agreement."

No one is willing to say what will happen if the board doesn't sign the new contract next week.

"We remain optimistic," Steele said. "We haven't planned our next step. We hope (the board) will do its job."